Ion implanters are commonly used in the production of semiconductor wafers. An ion source is used to create a beam of charged ions, which is then directed toward the wafer. As the ions strike the wafer, they impart a charge in the area of impact. This charge allows that particular region of the wafer to be properly “doped”. The configuration of doped regions defines their functionality, and through the use of conductive interconnects, these wafers can be transformed into complex circuits.
FIG. 1 is a block diagram of a plasma doping system 100, while FIG. 2 is a block diagram of a beam-line ion implanter 200. Those skilled in the art will recognize that the plasma doping system 100 and the beam-line ion implanter 200 are each only one of many examples of differing plasma doping systems and beam-line ion implanters that can provide ions. This process also may be performed with other ion implantation systems or other substrate or semiconductor wafer processing equipment. While a silicon substrate is discussed in many embodiments, this process also may be applied to substrates composed of SiC, GaN, GaP, GaAs, polysilicon, Ge, quartz, or other materials known to those skilled in the art.
Turning to FIG. 1, the plasma doping system 100 includes a process chamber 102 defining an enclosed volume 103. A platen 134 may be positioned in the process chamber 102 to support a substrate 138. In one instance, the substrate 138 may be a semiconductor wafer having a disk shape, such as, in one embodiment, a 300 millimeter (mm) diameter silicon wafer. The substrate 138 may be clamped to a flat surface of the platen 134 by electrostatic or mechanical forces. In one embodiment, the platen 134 may include conductive pins (not shown) for making connection to the substrate 138.
A gas source 104 provides a dopant gas to the interior volume 103 of the process chamber 102 through the mass flow controller 106. A gas baffle 170 is positioned in the process chamber 102 to deflect the flow of gas from the gas source 104. A pressure gauge 108 measures the pressure inside the process chamber 102. A vacuum pump 112 evacuates exhausts from the process chamber 102 through an exhaust port 110 in the process chamber 102. An exhaust valve 114 controls the exhaust conductance through the exhaust port 110.
The plasma doping system 100 may further include a gas pressure controller 116 that is electrically connected to the mass flow controller 106, the pressure gauge 108, and the exhaust valve 114. The gas pressure controller 116 may be configured to maintain a desired pressure in the process chamber 102 by controlling either the exhaust conductance with the exhaust valve 114 or a process gas flow rate with the mass flow controller 106 in a feedback loop that is responsive to the pressure gauge 108.
The process chamber 102 may have a chamber top 18 that includes a first section 120 formed of a dielectric material that extends in a generally horizontal direction. The chamber top 118 also includes a second section 122 formed of a dielectric material that extends a height from the first section 120 in a generally vertical direction. The chamber top 118 further includes a lid 124 formed of an electrically and thermally conductive material that extends across the second section 122 in a horizontal direction.
The plasma doping system may further include a source 101 configured to generate a plasma 140 within the process chamber 102. The source 101 may include a RF source 150, such as a power supply, to supply RF power to either one or both of the planar antenna 126 and the helical antenna 146 to generate the plasma 140. The RF source 150 may be coupled to the antennas 126, 146 by an impedance matching network 152 that matches the output impedance of the RF source 150 to the impedance of the RF antennas 126, 146 in order to maximize the power transferred from the RF source 150 to the RF antennas 126, 146.
The plasma doping system 100 also may include a bias power supply 148 electrically coupled to the platen 134. The bias power supply 148 is configured to provide a pulsed platen signal having pulse on and off time periods to bias the platen 134, and, hence, the substrate 138, and to accelerate ions from the plasma 140 toward the substrate 138 during the pulse on time periods and not during the pulse off periods. The bias power supply 148 may be a DC or an RF power supply.
The plasma doping system 100 may further include a shield ring 194 disposed around the platen 134. As is known in the art, the shield ring 194 may be biased to improve the uniformity of implanted ion distribution near the edge of the substrate 138. One or more Faraday sensors such as an annular Faraday sensor 199 may be positioned in the shield ring 194 to sense ion beam current.
The plasma doping system 100 may further include a controller 156 and a user interface system 158. The controller 156 can be or include a general-purpose computer or network of general-purpose computers that may be programmed to perform desired input/output functions. The controller 156 can also include other electronic circuitry or components, such as application-specific integrated circuits, other hardwired or programmable electronic devices, discrete element circuits, etc. The controller 156 also may include communication devices, data storage devices, and software. For clarity of illustration, the controller 156 is illustrated as providing only an output signal to the power supplies 148, 150, and receiving input signals from the Faraday sensor 199. Those skilled in the art will recognize that the controller 156 may provide output signals to other components of the plasma doping system and receive input signals from the same. The user interface system 158 may include devices such as touch screens, keyboards, user pointing devices, displays, printers, etc. to allow a user to input commands and/or data and/or to monitor the plasma doping system via the controller 156.
In operation, the gas source 104 supplies a primary dopant gas containing a desired dopant for implantation into the substrate 138. The gas pressure controller 116 regulates the rate at which the primary dopant gas is supplied to the process chamber 102. The source 101 is configured to generate the plasma 140 within the process chamber 102. The source 101 may be controlled by the controller 156. To generate the plasma 140, the RF source 150 resonates RF currents in at least one of the RF antennas 126, 146 to produce an oscillating magnetic field. The oscillating magnetic field induces RF currents into the process chamber 102. The RF currents in the process chamber 102 excite and ionize the primary dopant gas to generate the plasma 140.
The bias power supply 148 provides a pulsed platen signal to bias the platen 134 and, hence, the substrate 138 to accelerate ions from the plasma 140 toward the substrate 138 during the pulse on periods of the pulsed platen signal. The frequency of the pulsed platen signal and/or the duty cycle of the pulses may be selected to provide a desired dose rate. The amplitude of the pulsed platen signal may be selected to provide a desired energy. With all other parameters being equal, a greater energy will result in a greater implanted depth. The plasma doping system 100 may incorporate hot or cold implantation of ions in some embodiments.
Turning to FIG. 2, a beam-line ion implanter 200 may produce ions for treating a selected substrate. In one instance, this may be for doping a semiconductor wafer. In general, the beam-line ion implanter 200 includes an ion source 280 to generate ions that form an ion beam 281. The ion source 280 may include an ion chamber 283 and a gas box containing a gas to be ionized. The gas is supplied to the ion chamber 283 where the gas is ionized. This gas may be or may include or contain, in some embodiments, hydrogen, helium, other rare gases, oxygen, nitrogen, arsenic, boron, phosphorus, carborane, aikanes, or another large molecular compound. The ions thus generated are extracted from the ion chamber 283 to form the ion beam 281. A power supply is connected to an extraction electrode of the ion source 280 and provides an adjustable voltage.
The ion beam 281 passes through a suppression electrode 284 and ground electrode 285 to mass analyzer 286. Mass analyzer 286 includes resolving magnet 282 and masking electrode 288 having resolving aperture 289. Resolving magnet 282 deflects ions in the ion beam 281 such that ions of a desired ion species pass through the resolving aperture 289. Undesired ion species do not pass through the resolving aperture 289, but are blocked by the masking electrode 288.
Ions of the desired ion species pass through the resolving aperture 289 to the angle corrector magnet 294. Angle corrector magnet 294 deflects ions of the desired ion species and converts the ion beam from a diverging ion beam to ribbon ion beam 212, which has substantially parallel ion trajectories. The beam-line ion implanter 200 may further include acceleration or deceleration units in some embodiments.
An end station 211 supports one or more substrates, such as substrate 138, in the path of ribbon ion beam 212 such that ions of the desired species are implanted into substrate 138. The substrate 138 may be, for example, a silicon wafer or a solar panel. The end station 211 may include a platen 295 to support the substrate 138. The end station 211 also may include a scanner (not shown) for moving the substrate 138 perpendicular to the long dimension of the ribbon ion beam 212 cross-section, thereby distributing ions over the entire surface of substrate 138. Although the ribbon ion beam 212 is illustrated, other embodiments may provide a spot beam.
The ion implanter 200 may include additional components known to those skilled in the art. For example, the end station 211 typically includes automated substrate handling equipment for introducing substrates into the beam-line ion implanter 200 and for removing substrates after ion implantation. The end station 211 also may include a dose measuring system, an electron flood gun, or other known components. It will be understood to those skilled in the art that the entire path traversed by the ion beam is evacuated during ion implantation. The beam-line ion implanter 200 may incorporate hot or cold implantation of ions in some embodiments.
As stated above, ion implantation is a standard technique for introducing conductivity-altering impurities into semiconductor substrates. A desired impurity material is ionized in an ion source, the ions are accelerated, and the ions are directed at the surface of the substrate. The energetic ions penetrate into the bulk of the semiconductor material. Following an annealing process, the ions may become incorporated into the crystalline lattice of the semiconductor material to form a region of desired conductivity.
Silicon or other materials may also have an amorphous crystal structure. In a silicon substrate, one silicon atom is usually tetrahedrally bonded to four neighboring silicon atoms and these silicon atoms will form a well-ordered lattice across the substrate. In contrast, this order does not exist in amorphous silicon. Instead, the silicon atoms form a random network and the silicon atoms may not be tetrahedrally bonded to four other silicon atoms. In fact, some silicon atoms may have dangling bonds.
Amorphizing implants, such as a pre-amorphizing implant (PAI), are used to amorphize the crystal lattice of a substrate. Prior to the amorphizing implant, the substrate usually has a crystal lattice with a long-range order. Such a structure allows implanted ions to move through the crystal, or channel. By amorphizing the substrate, channeling of dopants, or implantation of ions substantially between the crystal lattice of the substrate, during later implantation may be prevented or reduced because the substrate will lack a long-range order. Thus, the dopant implant profile may be kept shallow.
Previously, USJ formation had been performed with a PAI using heavier species such as germanium and silicon to prevent channeling. This method may cause residual damage at the end of range and subsequent leakage in complementary metal oxide semiconductor (CMOS) transistors. Yet, if the PAI step was removed, channeling of ions will occur, thereby increasing the junction depths. Additionally, advances in USJ have required annealing technologies capable of millisecond (MS) thermal budgets near a target temperature. A MS anneal is unable to completely remove implant damage caused by silicon or germanium PAI, and specifically end of range (EOR) defects. Furthermore, there is a lack of lateral diffusion of a dopant in the substrate. This lack of lateral diffusion may cause overlap capacitance issues within a device.
Accordingly, there is a need to improve the implantation methods used to form USJ and, more particularly, there is a need to create methods using helium to form ultra shallow junctions.